Steering performance is well known to be critical in rolling mills such as steckel mills. A steckel mill equipped with hydraulic gap control has the potential for automatic steering control through differential cylinder-adjustment. Conventionally, steckel operators steer the mill by watching for deviations of the strip running line from the centre line of the mill, and adjusting the differential roll gap to counteract this. However, this method can lead to over-steering and as a result the strip carries not only a high risk of cobbles, but also other difficulties, leading to long outages in clearing the line afterwards.
The conventional method of automatic steering is to apply a differential roll gap correction according to a measured differential load. The effectiveness of this method depends on the source of error. If there is a difference in temperature (and thus resistance to deformation) across the stock it generally works well, acting to keep elongation equal at the two edges. The bar then remains straight. If the stock has a wedge profile, with one side larger than the other, however, the system will tend to equalise the edge thicknesses but in doing so produces a cambered bar. A steering system based on load difference is thus limited in performance by an inability to discriminate between these two sources of error.
It is an objective of the invention to provide effective control, thus leading to benefits in mill stability and dimensional variability, particularly in eliminating the problems associated with the rolling of wedge shaped product.